1. Field of the Invention
The present invention generally relates to a method for driving an optical deflecting device capable of changing a direction an output light with respect to an input light, and for example, relates to a technology suitable for an image forming apparatus such as a printer, a copier, or a like applying of an electrophotographic method, and a projection type image video displaying apparatus such as a projector, a digital theater, or a like.
2. Description of the Related Art
For example, L. J. Hornbeck proposed a digital micromirror device of a torsion beam hinge (see “Proc. SPIE Vol. 1150, pp. 86-102 (1989)”). Moreover, a space light modulator having a micromirror group, in which a technology of the digital micromirror device has been developed, is called a DMD (Digital Micromirror Device), and used in an image projection apparatus (for example, see “Proc. of the IEEE, vol. 86, No. 8, pp. 1687-1704 (1998)”).
These devices are supported by torsion beams in which a mirror is generally called a hinge. By using the hinge, a reflection area can be reduced. On the other hand, in the described-above DMD, a reflection member is provided to a surface in addition to a hinge portion, and a two-step structure. Moreover, although a voltage to actually drive becomes dozens of volts by using the hinge, in order to control with 5V through 7.5V as data for switching an inclination direction, an inclination switch is conducted by combining a bias voltage being dozens of volts being simultaneously applied to a plurality of pixels and restoration force of a special spring member.
Moreover, as described in Proc. SPIE Vol. 1150, pp. 86-102 (1989), a driving method for changing an electronic potential of a mirror is disclosed. Compared with a monostable operation, a bidirectional operation of a mirror having a larger deflection angle is advantageous. In order to acquire a bistability, a hinge being rigidly connected to a mirror is used. The above-described driving method proposes a method for changing a voltage of an electrode facing to the mirror simultaneously with a voltage of the mirror.
In addition, the applicant of the present invention previously proposed the following optical deflecting device. That is, Japanese Laid-open Patent Application No. 2004-78136 discloses an optical deflecting device for changing an electrostatic attraction corresponding to an electric potential being applied to a member having a light reflection area, and changing a reflection direction of an incoming light flux and deflecting the incoming light flux entering the light reflection area, the optical deflecting device including a substrate; a plurality of controlled members; a fulcrum member; and a plate member 107a, wherein each of the plurality of control members has a stopper at an upper portion, and the plurality of control members are respectively arranged at a plurality of edges of the substrate; the fulcrum member includes an apex configured by a conductive member, and is arranged on an upper surface of the substrate; the plate member does not have a fixed end, but has the light reflection area on an upper surface of the plate member, has a conductive layer formed by a member partially being conductive at least, is configured by a member having a conductive contact point at least contacted to the apex of a rear surface of the plate member, is movably arranged in a space formed by the substrate, the fulcrum member, and the stopper, and wherein an electric potential of the plate member is applied by a contact with the fulcrum member, an arbitrary electric potential is applied to each of the plurality of electrodes so that a maximum electric potential difference becomes greater than a predetermined voltage, and an electric potential applied to the apex is set to be equal to either one of a maximum value and a minimum value which are applied to the plurality of the electrodes.
A spatial light modulator or an optical deflecting device using the above-described hinge has restoration force due to stiffness, and a drive voltage becomes up to dozens of volts. On the other hand, high precision is desired for a high definition television set, a high resolution television set, and a like. In a case of increasing the number of pixels, a chip size becomes larger, a process flow becomes specialized, and a material cost is increased. Accordingly, it is required to minimize the size of a mirror forming a pixel. Consequently, a stiffness of the hinge suspending the mirror becomes greater, and the drive voltage is increased. Moreover, in a case of minimizing the size of the mirror, it is not easy to reduce the stiffness due to a limitation of precision of a micro process to thin down the hinge. Even if its usage is not required to be minimized, the hinge is bent down in a case of reducing the stiffness and the drive voltage. As a result, a center position of the mirror cannot be maintained. Also, in a case of using the hinge, the hinge is formed on a surface of the mirror. Then, an area for reflecting light is reduced.
Accordingly, a reflective surface is formed on a driving electrode, and a double structure is formed. This configuration increases the reflection area and becomes complicated. Therefore, in a case of a configuration using the hinge, minimizing causes that a device configuration becomes complicated and manufacturing costs increase.
Moreover, as a method for conducting a bistable operation using a hinge, Japanese Laid-open Patent Application No. 5-150173 discloses a method for switching an inclination of a mirror by cooperatively actuating a first electric potential of the mirror and an electric potential of an electrode. A beam is a torsion beam, and the restoration force of the stiffness of the hinge is mandatory to be used. There is a problem that the mirror as a beam cannot rotate without a torque. In a case in that an inclination direction of the mirror is changed, when a switch signal is input to either one of two-way directions, a direction is similarly changed. However, in order to switch an inclination direction by an electric potential of approximately 5V that is generally an operation voltage of an LSI (Large Scale Integration), since there is an unstable state due to a balance between a stiff restoration force and an electrostatic force, a switch of the inclination direction is limited to a narrow range of the driving voltage. Furthermore, it is difficult to combine with the LSI which operates at approximately 3.3V as the driving voltage. Also, there is another problem in that the beam immediately operates when data are written. This occurs since a display period is influenced if a data write is delayed. In addition, in the configuration using the hinge, an inclination is made based on one axis alone by using the hinge. As a result, an light deflection is made based on one-axis direction alone.
On the other hand, in the optical deflecting device (disclosed in Japanese Laid-open Patent Application No. 2004-78136), a plate member having a light reflection area does not have a fixed end such as a hinge or a hinge being less rigid is used, it is possible to easily conduct a bistable switch. Electrodes electrically contacted to a conductive layer of the plate member and electrodes facing to the plate member are divided into two groups with respect to a fulcrum member, an arbitrary electric potential is applied to each of electrode groups, and an electric potential of the electrodes electrically contacted to the conductive layer of the plate member is switched. Accordingly, it is possible to easily switch an inclination direction of the plate member.
Moreover, in a configuration in which the plate member does not have a fixed member such as a torsion beam, the inclination direction of the plate member can be changed based on two axes by a configuration of the electric potential being applied to a plurality of electrodes. Since stiffness of the torsion beam is not used, further precision can be easily realized.
However, even in a case in that a control electric potential applied to each of the electrode groups is a direct driving voltage and an LSI memory is used, if a response time of the plate member is less than 5 μsec., a voltage of more than 10V is required. In a case of configuring an image displaying apparatus by combining with the LSI memory, a dedicated driving device of a higher voltage is required.